The aim of this research is to provide information about how the ability to learn and remember changes during development. It is guided by a recent theory of how the hippocampal formation contributes to learning and memory. This theory, termed configural association theory, distinguishes between an elemental associative system and a configural associative system. The configural system is assumed to enable the organism to construct a representation of stimulus conjunctions that can control learned behaviors and to depend on the hippocampal formation. Without a functioning configural system there are many ways in which an organism would be at a disadvantage. Based on (a) the generally accepted idea that, at least in the rat, the hippocampus is late to mature, and (b) existing behavioral data, it is proposed that the configural system develops late in comparison to the elemental association system. This developmental hypothesis has important and testable implications for the adaptive strategies that are available to different-aged animals. The proposed research will test the hypothesis with rats. Implications of the hypothesis will be evaluated in relation to several general issues: (a) Can different-aged rats solve nonlinear discrimination problems, such as the transverse patterning problem? (b) How do different-aged subjects (17 to 35 days old) resolve conflicting memories? (c) How do different-aged rats neutralize irrelevant environmental stimuli? (d) How do different-aged rats solve problems (e.g., the feature positive problem) when one of the stimulus elements is ambiguous but the problem permits both elemental and configural solutions. The developmental hypothesis predicts that young animals will not be able to (a) solve the transverse patterning problem, (b) resolve conflicting memory problems, or (c) to neutralize irrelevant cues that can interfere with discrimination learning. On the other hand, it allow that animals will be ale to solve relatively complex problems that have elemental association solutions.